Apparatus and process for solvent extraction



L.. D. KLExss 2,911,361

-APPARATUS AND PROCESS FOR SOLVENT EXTRACTION Nov. 3, 1959 Filed Feb. 25, 1955 m .r ON- INVEN TOR.

A TTORNE VS :United States Patent() s Y 2,911,361' Patented Nov. 3, 1959 APPARATUS'AND PROCESS FOR SOLVENT EXTRACTION Louis.D. Kleiss, Phillips, Tex., assgn'or to Phillips Petroleum Company, a corporation of'Delaware Application Ilebruary l25, '1955, Serial N o. 490,525

514 Claims. (Cl. 208-311) L' This invention relates to. a process and arrangement of yapparatus for effecting solvent extraction of liquid mixtures and separation of the same into their components. Aspecific aspect of the invention pertains to amethod and apparatus for controlling a solvent extraction process.

The separation of liquid mixtures of organic materials and particularly hydrocarbon compounds into two or more fractions of different characteristics by solvent extraction and recovery ofv thev separated compounds from the solventfhaslongheen practiced.' As applied to hydrocarbons the selectiversolvent utilized usually has a greater anity ,for more cyclic and/ orfuns-atu'rated hydrocarbons inia,s erli'esY of hydrocarbonsrof'similar molecular weight. Inconventional solvent extraction processesv one of the tionl are difiicult to obtain. Pressure surgeswithin the zequipment are. frequent and of considerable magnitude, vthereby throwing the process out of control and requiring considerable time to bring the process back on smooth operation and the product stream orstreams up,l to the desired standard of purity or componentconcentration;

' One of the principal objects of they invention is to provide a process and arrangement of apparatus forthe efficient separation of the components of a liquid mixture, utilizing av selective solvent for` oneor more of the cornponents. vAnother object is to provide a process and apparatus for effecting liquid-liquid extraction of a liquid mixture with accurate and close control ofthe ow of streams to and from the extraction column. It is also van object of the invention to provide a process and arrangement. ofV apparatus for effecting liquid-liquid extraction which prevents surging and pressure pulsations within the extraction equipment. A further object of the invention is to provide a process and arrangement of apparatus for separating a hydrocarbonmixture -into selectedy hydrocarbon fractions byVliquid-liquid extraction with a selective solvent whereby accurate and close control of the character of the selected-hydrocarbon fraction is afforded; Other objects of the invention will become apparent from a consideration of the accompanying disclosure.

The invention is applicable to the conventional solvent extraction processes of the prior art and comprises an arrangement of apparatus with controls and a method of operation for controlling a solvent extraction process so as to maintain substantially uniform and smooth process conditions throughout the extraction and separation system.

vIn accordance with the invention, the, various streams flowing to and from a liquid-liquid extraction process,

with the exception of the solvent feed stream and the extract product stream, are maintained on substantially constant flow. The rate of flow of solvent feed to the extraction column is varied to supply the required amount of solvent to extract the desired amount of extract material under unavoidably fluctuating process conditions including temperature, pressure, feed composition, etc. The essential feature of the invention comprises varying the solvent feed rate under reasonably uniform process condi,-

tions to maintain a substantially constant solvent-rafinate l interface-level in the `column. If thefeed to be extracted is fed at a constant rater to a steady state column and-.a smaller` stream of raffinate is'removed from the topy of the column, the balance of the feed stream must be removed by solution inthe solvent. .The amount of solvent (ow rate) needed varies with fluctuations in temperature, pressure, liquid compositions, and reflux rate. The correct solvent rate causes the rainate-solvent interface level to .stabilize and, hence, this interface may be sensed by a liquid-level-controller and utilized to control the solvent feed rate.

-In a preferred embodiment of the invention the rate of `flow of feed, raffinate product, raiiinate recycle, and ex' tract recyclel or reflux are maintained constant -by any suitable means, such as a metering vpump or constant j iow control valve; the extract phase (solvent plus extracted material) is maintained onv pressure control; and the ex? tract product is maintained on liquid level control of the solvent fractionator overhead product accumulator. The solvent stream isV preferably saturated with raffinate comf ponents prior to entry into the extractive column by adf mixture vwiththe'raffinate recycle stream. In this-method of operation, it is desirable to maintain the temperature of theinlet streams relatively constant.

In one embodiment of the invention, the extraction Vcolumn is divided. into two or more sections which are `operated as separate extraction zones arranged in series,

the intermediate extract phase taken from the bottomof the first column or section to which the feed is introduced being passedV to the upper portion of the second section, and the intermediate raffinate taken from the top of the second section being introduced to the lower portion of the first section, and` so on with any number of sections'. These separate sections may be considered as extraction columns operated in series.

The process of the invention comprises passing a feed stream including a plurality of liquid componentsl into an intermediate section of an extraction zone; passing a solvent stream comprising a selective solvent for at least one of the components of the feed into an upper section of the extractionzone so as to effect commingling of the feed and solvent and extraction of at least one of the feedlcomponentsto form a solvent-extract phase and a raffinatel phase lean inthe extract and establish an interface in the extraction zone between the phases; recovering a ranate stream from the uppermost section of the extraction zone; recovering a solvent-extract stream from the lowermostY section of the extraction zone; separating the solventextract stream into a solvent stream and a concentrated extract stream; separating the concentrated extract stream into an extract product stream and an extract recycle stream; recovering the extract product stream andk ref cycling the extract recycle stream to the extraction zone as reflux; and. controlling the operation of the extractionzoney by the steps comprising maintaining a substantially' constant ow of feed, raiiinate, and extract recycle, andy varyingthe flow rate of the solvent stream so as to maintain, a substantially constant interface between the. ,solventi and raffinate in the extraction zone.

- `Illustrative-of the processes to which the invention is applicable are the separation of cycloparafns such as cyclohexane from a mixture of the same with parafins; separation of aromatics from a mixture with paraflins; separation of aromatics from a mixture with naphthenes and paraffins; and separation of aromatics and naphthenes 'from a mixture with paralins. Commonly used selective solvents include methyl Carbitol, furfural, methanol, diethyleneglycol, triethyleneglycol, acetonitrile, sulfur dioxide, and their aqueous solutions. Alcohol and other solubility modifying agents may be used.

A more complete understanding of the invention may Vbe had from a consideration of the accompanying drawing which is a ow diagram illustrating one embodiment of the invention.

' lReferring to the drawing, the apparatus includes an upper extraction column andalower extraction column 12 together with a steam distillation or fractionation column 14 and a phase separator 16 connected by lines hereinafter described. A feed line 18 including a ow control device 20, such as a metering pump, connects with the lower section of column 10 for introduction of feed thereto at a constant rate. A solvent feed line 22 having positioned therein a iiow control valve 26 connects with an intermediate section of column 10 for introduction of solvent thereto at a controlled rate. A liquid-level-controller 27 sensitive to the raffinate-solvent interface level in column 10 regulates valve 26 so as to maintain a constant 'interface level. A temperaturerecorder-controller 28 connected with line 22 near column 10' operates a ow control valve 30 in a steam line 32 which passes steam thru a heater 34 in line 22. This arrangement permits heating the solvent stream to the proper temperature for introduction to column 10.

A raihnate efliuent line 36 enters a surge tank 38 'om which a railinate product line 40, containing metering or llow .control device 41, passes to suitable disposal. A raffinate recycle line 42 having positioned therein a ow control device 44 connects with solvent feed line 22 upstream of iiow control valve 26. A solvent-extract effluent line 46 connects the bottom ofkcolumn 10 with an intermediate section of column 12 for delivery of intermediate solvent-extract thereto. An intermediate rafiinate effluent line 54 connects the top of column 12 with feed line 18. Line 54 may also connect directly with the lower section of column 10. A liquid or interface-levelcontroller 56 sensitive to the interface level in the upper section of column 12 is operatively connected to avow control valve 58 in line 54 so as to maintain a substantially constant interface level in column 12 by regulating the ow of intermediate rainate to column 10.

A line 60 connects the bottom of column 12 with an intermediate section of a steam distillation column 14 thereby providing flow of solvent-extract from extraction column 12 to separation column 14. A ow control valve 62 positioned in line 60 is operatively connected with a pressure-recorder-controller 64 which is sensitive to pressure in column 12 and operates valve 62 so as to maintain a selected predetermined pressure in column 12. A heater 66 positioned in line 60 near column 14 provides for heating the solvent-extract stream to the proper temperature for introductionat a corresponding temperature point in column 14. A solvent recycle line 68 connects the `bottom of column 14 with lean solvent surge tank 69 which is also connected with solvent feed line 22. Flow of solvent in line 68 is regulated by ow control valve 70 operatively connected with liquid-level controller 72 which is responsive to the liquid level in the lower section of column 14' and regulates the flow of lean solvent in line 68 so as to maintain a substantially constant liquid level. Temperature control of the lean solvent in line 68 is provided by cooler 73, as desired.

^ Heat for operation of steam distillation column 14.y is provided by recycle line 74 which passes thru heater 76 and returns to column 14. Water for the steam distillation is supplied by line 78 which connects with line 74 upstream of heater 76. A temperature-recorder-controller 80 sensitive to temperature in column 14 is operatively connected to a ow control valve 82 in a steam line 84 which passes steam thru heater 76 in indirect heat exchange with the liquid passing thru line 74, including water from line 7S. The lean solvent stream 68 leaving column 14 is saturated with Water at the temperature and pressure existing within the lower section of the column, and the water content of the solvent is controlled by adjustment of temperature-recorder-controller 80. An alcohol or other liquid may be used instead of Water'as a stripping agent and to modify the solvent power of the solvent.

A cooling coil 86 positioned in the upper section of column 14 provides internal reux for this column. An efuent line 88 connects with the top of column 14 and with an intermediate section of phase separator 16 for passage of distilled vapor into condenser 90 and thence into separator 16 where the extract containing entrained water is separated into a water phase 92 and an extract phase 94. A vent line 96 connects with the top of separator 16 for the withdrawal of uncondensed vapor from the system.

Extract is recycled via line 98 at a steady predetermined rate under the control of ow controller 100 and valve 101 to the lower section of column 12 as reux. The remaining portion of the rich extract is withdrawn thru line 102 on overow from accumulator or separator 16. Water is withdrawn from the water phase 92 in separator 16 thru line 78 at a constant rate by means of flow control device or metering pump 109 positioned in line 78, and the flow rate is periodically regulated by resetting pump 109 so as to maintain a suitable interface (or water) level in separator 16. However, an interfacelevel-controller on separator 16 may be utilized to control the ow of Water in line 78 to automatically maintain the desired water level in the separator.

`Control of the temperature of the extract recycle stream is provided by a heater 110 positioned in line 98.

A heating fluid, such as steam, is passed thru the heaterV via line 111 under the control of valve 112 which is operated by temperature-recorder-controller 114 which'in turn is sensitive to the temperature in line 98 and regulates the heating in heater 110 so as to provide a `suitable predetermined temperature in the extract recycle stream.

Line 116 connects with lean solvent surge tank 69 so as to provide for replenishing the supply of solvent for the process. A number of ow indicating elements 118 are provided in some of the lines for measuring the flow in these lines at any particular time. Several temperature recorders 120 are connected at various points in the system for determining temperature. Several pumps 122 are shown positioned in the various lines to effect the desired flow and pressure in those lines. Other pumps and indicating devices may of course be utilized where needed. Steam distillation column 14 may be replaced by another type of distillation means, and the solvent power of the solvent may be adjusted by contacting with water or other agent under controlled conditions, or by ratio ilow control of solvent and modifying agent.

The invention is not limited to any speciiic instruments but is broad enough to Vencompass any instruments which have the designated function or functions. The invention is rather in an arrangement of apparatus elements which effect the process control disclosed and in the process control steps practiced as disclosed.

The following examples are set forth to illustrate the invention and its applicability to different systems. The data given represent spot determinations under steady state conditions. The proportion of recycle extract to product was varied as conditions required in order to maintain substantially constant extract product composition. The data and examples are illustrative and should metering pump 20.

` notbe interpreted as unnecessarily limiting the invention.

EXAMPLE I The apparatus shown -in the drawing was utilized in `separating a normal octane concentrate from a mixed 4'hydrocarbon feed containing principally CB to C10 paraffins, aromatics, and naphthenes, as shown in Table 1 below, utilizing Wet methyl Carbitol as a solvent. The extraction columns were 4" in diameter and 30' long and 4were packed in conventional manner with 25.5 of 1/2" f ViBerl saddles. Approximately A1155 pounds of 70+ liquid volume percent C8 parailins (8S-89 liquid volume percent Ca-Cm paraflns) was made from 2042 pounds'of feed in a two-pass extractionwith wet methyl Carbitol. In

' the extraction, approximately 90% of the C8 naphthenes and essentially lall of the aromatics contained in the feed -Wereremoved in the extract product.

More complete data for the runare shown in Table 1 below.

The extract from the first pass (shown in Table 1) rwas introduced `to column 12 at an intermediate point vtherein at the rate-of 1.30 g.p.h. under the control of `Methyl -Carbtol containing 2.2 zliquid volume `percentJ-Water Wasintroduced by line'22 Vinto column 10 at an average rate of about 46 g.p\.h. and

"thisstrea'malsoincluded `5.0 g.p.h. `-of`recycle raflinate '-'meter" by pump 44. This ow rate of solvent in line 22 Twas regulated bylevel controller 27 controlling valve *.10 varied from about 116 F. at the bottom to 118 F.

:at the top and -the bottom temperature in column 12 Was' about 108 F.

PreSsure-recorder-control]er 64 was set to'maintain -a pressureof. 18,p.s.i.g'. in column 12 and this pressure was substantially maintained during the run.

i trol.

. Table 2 Hydrocarbon Ranate Feed Product Recovery of Y n-Nonane 5 Run No. Reflux in Wt. Mol per- Ratio Ratnate, g.p.h. percent g.p.h. cent npercent n-Nonane Nonane by F.P.

EXAMPLE III 15 I Runs were made utilizing the control and separation 'system substantially as shown in the drawing in the separation of naphthenes (mainly dimethylcyclopentanes) from parans (mainly 2 and 3 methylhexenes). In a typical run the feed contained 49.7 LV percent naphthenes and was introduced at an intermediate point to column 12 at the rate of 1.48 g.p.h. Methyl Carbitol solvent containing 3 to 5 liquid volume percent water was fed at an average rate of 62.8 g.p.h. together ,with a constant raffinate recycle of 5.0"g.p.h. into vthe upper section of column 10. The interface level Vin .column 10 was maintained substantially constant by level controller 27 which passed the krequired amount of solvent and ranatezrecycle thru valve 26 to effect this con- Rainate product containing 0.7 LV percent naphthenes was recovered at the rate of 0.57 g.p.h. under the control of metering pump 41. Extract product containing 71.7 LV percent naphthenes was recovered at the average rate of 0.91 g.p.h. on overow from accumulator 16. The rate of extract recycle in line 98 Was maintained constant at 8.16 g.p.h. by now-controller 100. The flow ratio was `8.80 and the reiiux ratio was 8.97.

The pressure in the bottom of column 12, as indicated by instrument 64, was 18.2 p.s.i.g. The temperature in the bottom of column 12 was 121 F. and the temperavture in the top of column 10 was 134 F. The temperature of the stream in line 22 between heater 34 and column 10"was maintained at 138 F. yThe temperature of jthestream in line was maintained at 120 F. by heater Table 1 Liquid Volume, Percent l i Sp.Gr i

Y Material 20/4 Parans Aromatics Naphthenes Ca C9 C10 C7 C3 C9 C10 CB CU C10 Feed'. 0. 7449 45.1 14. 8 0.9 0.5 11. 4 1. 5 0.1 18. 7 6.4 0.6 1st Pass Ranate 0. 7156 V72. 0 16.3 1. 1 0.0 1. 6 0.5 0.2 2.8 4. 6 0.9 1st PaSS`Extract.- 0. 7711 34. 6 6. 7 0. 6 0. 7 19. 1 2. 1 0. 1 28. 9 6. 9 0.3 2nd Pass Ranate O. 7167 69 1 15. 6 0, 9 0. 0 1. 0 0. 6 0. 2 2. 6 9. 3 0. 8 :2nd-Pass Extract. 0.8052 2 6. 4 36. 7 4 56. 9

' Vl VCalculated from mass spectre analysis.

'I Total parans by PONA analysis. @Total aromatics by PONA analysis.

4 Total nap'hthenes'byPON A analysis.

' EXAMPLE n *Several lruns Were made in a liquid-liquid extraction AAsystem l'arrangedl substantially. as shown in the drawing .utilizing a.y ffeed'containing' 73% normal nonane and a `methyl Carbitol sol-vent containing from Sfto 5 Weight 'percent Water. Approximately 337 pounds -of 976+ mol :percent n-nonane Vwas made from 681 Vpounds of l73% n-nonane-in the runs. The overall recovery of n-nonane `contained in the feed as ralinate product was approxi- .mately percent, the highest `recovery in a single run being 82.3%.

l The methodof operation was similar to that described vin Example I. Data obtained in three representative runs are shown in Table 2.

66 and the temperature of the extract recycle entering column 12 via line 98 was maintained at 110 F. by heater 110.

In the various runs made in the examples with the system andk arrangement of controls shown and described, exceptionally smooth operation was encountered.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative "details disclosed are not to be construed as imposing unnecessary limitations on vthe invention.

I claim: p

`1. In solvent extraction lapparatus comprising an extraction column; a feed line leadinginto an intermediate 'section' ofsaid column having 110W Vcontrol means; a

valved solvent feed line leading into an upper section of said column; a raflnate takeoff line connected with the tion of said column, the improvement comprising means for controlling the rate of raffinate takeof at a substantially constant value and means for varying the solvent input rate in response to the rise and fall of an interface between solvent and raffinate phases so as to stabilize said interface.

2. Apparatus for effecting liquid-liquid extraction of armixed feed stream, comprising a liquid-liquid extraction column; a feed line leading into an intermediate section of said column having means for controlling the rate of flow therein; a solvent feed line leading into an` upper section of said column having means for controlling the rate of flow therein; a raffinate line leading from the uppermost section of said column having flow control means therein; an interface-levelcontroller sensitive to an interface level in an upper section of said column at a level above said solvent feed line in operative contr'ol of the flow-control means in said solvent feed line;

Va solvent-extract line leading from the lowermost section of said column; means in said solvent-extract line forseparating solvent-extract into a solvent stream in a solvent effluent line and an extract stream in an extract efuent line; an extract recycle line for passing extract effluent to a lower section of said column; and

means for controlling the rate of flo-W in said extract recycle line.

3. The apparatus of claim 2 including a variable flowcontrol means in said solvent-extract line upstream of said means therein; a pressure-controller sensitive to pressure in said column and in operative control of last said means.`

4.` The apparatus of claim 3 wherein said means in said Solvent-extract line comprises a steam stripping columnV having a line for introducing steam into a lower section thereof, an extract effluent line from an upper section thereof, and a solvent recycle line from the lowermost section thereof connecting` with said solvent feed line; a ow control valve in said solvent recycle line; a liquid-level-controller sensitive to a liquid level in a lower section of said stripping column in operative control of last said valve; a phase separation vessel in said extract efuent line having an extract product line and sltreamsand extraction of at least one of said Icomponents 'i to form a solvent-extract phase and a ranat phase Vlean in said extract and establish an interface between the phases; withdrawingl `a rainate stream from the top of i saidcolumn; and withdrawing a solvent-extract stream from the bottom of said column; the improvement comprising withdrawing said raffinate stream at a substantially constant rate and varying the flow rate of said stream of solvent in response to the rise and fall of said interface so as to hold said rise and fall to a minimum.

9. A liquid-liquid extraction process comprising passing a feed stream comprising a plurality of liquid components into an intermediate section of an extraction y zone; passing a solvent stream comprising a selective an extract recycle line leading from an intermediate section thereof, said extract recycle line connecting with Y for flow of raffinate from each downstream column to the next upstream column.

7. The appara-tus of claim 2 wherein said extraction column comprises at least two separate Vessels connected in series for flow of solvent-extract from the feed column toward the next downstream column in each instance and for ow of raffinate from each downstream column to the next upstream column.

8. In a solvent extraction process comprising passing a liquid feed stream of a plurality of components into an intermediate section of an extraction column at a substantially constant rate; passing `a stream of selective solvent for at least one of said components into an upper section of said column so as to effect comminglling of said solvent for at least one of said components into an upper section of said extraction zone so as to effect commingling of said streams vand extraction of at leastone of said components to form -a solvent-extract phase and a raffinate phase lean in said extract and establish an interface in said zone between said phases; withdrawing a rainate stream from the uppermost section of said zone; withdrawing a solvent-extract stream from the lowermost section of said zone; separating said solvent-extract stream into a solvent stream and a concentrated extract stream; separating said concentrated extract stream into an extract product stream andan extract recycle stream; recovering said extract product stream and recycling said extract recycle stream to `a lower section of said zone as reflux; and controlling the operation of said process by the steps comprising maintaining the ow rates of said feed stream, said rainate stream, and said extract recycle stream substantially constant, and varying the ow rate of said Asolvent stream so as to maintain a substantially constant Lsolvent-raffinate interface in said zone.

10. The process of claim 9 including the step of controlling the ow rate of said solvent-extract stream so as to maintain a predetermined pressure in said zone.

1l. The process of claim l0 including the steps of scparating said solvent from vsaid solvent-extract stream in a steam distillation zone wherein said solvent is recovered las bottoms; regulating the iiow rate of solvent from said distillation zone so as to maintain 4a substantially constant solvent liquid level therein; and recycling said solvent to said extraction zone.

l2. The process of claim l0 including recycling a portion of said raffinate stream at a substantially constant rate to said zone.

13. A liquid-liquid extraction process comprising passing -a feed stream comprising a plurality of liquid components at a constant rate into one of a plurality of extraction zones connected in series; passing a liquid solvent stream comprising a selective solvent for at least oneV o f said components into an upper section of the first of said zones; effecting commingling of said feed and said solvent in said zones so as to extract at least one of said components thereby forming a solvent-extract phase and a raffinate phase lean in said extract and establishing an interface between said phases in each of said zones; passing said rallinate phase toward the'u'pperend Aof said first zone and said extract phase toward the lower end of the last of said zones; withdrawing a raffinate stream from the upper sec-tion of said first zone at a constant rate; withdrawing a solvent-extract 4stream-from the lower section of said last zone at such a rate as to maintain a predetermined pressure in saidr zones; regulating the flow to one of said zones as reux; and recovering the re- -mainder of said extract stream as product.

14. 'Ihe process of claim 13 including operating said fractionation zone asa steam distillation zone so as to recover an -aqueous extract stream overhead and a kettle fraction comprising solvent; withdrawing solvent from .the lower section of said fractionation zone at such a rate as to maintain `a desired liquid level in said fractionation zone; eecting separation of said aqueous extract stream into an aqueous phase and an extract phase in a phaseseparation zone; withdrawing a portion of said extract phase as said product stream and the remaining portion as said extract-rich recycle stream.

References Cited in the file of this patent UNITED STATES PATENTS 1,601,320 Peters Sept. 28, 1926 .Grote et al. Nov. 27, 1934 Archibald Feb. 8, 1938 Tijmst-ra Aug. 6, 1940 Carney Mar. 24, 1942 Rosebaugh Oct. 20, 1942 Pierotti et al Oct. 24, 1944 Cummings et al Mar. 12, 1946 Wagner Feb. 18, 1947 Gilmore Oct. 6, 1953 v Weedman Nov. 23, 1954 McCauley Dec. 27, 1955 Grunewald May 22, 1956 Poenberger Aug. 20, 1957 Morrison et al Apr. 15, 1958 Ratje et al Oct. 7, 1958 

1. IN SOLVENT EXTRACTION APPARATUS COMPRISING AN EXTRACTION COLUMN; A FEED LINE LEADING INTO AN INTERMEDIATE SECTION OF SAID COLUMN HAVING FLOW CONTROL MEANS; A VALVED SOLVENT FEED LINE LEADING INTO AN UPPER SECTION OF SAID COLUMN; A RAFFINATE TAKEOFF LINE CONNECTED WITH THE TOP OF SAID COLUMN HAVING FLOW CONTROL MEANS; AND A SOLVENT-EXTRACT TAKEOFF LINE CONNECTED WITH A LOWER SECTION OF SAID COLUMN,THE IMPROVEMENT COMPRISING MEANS FOR CONTROLLING THE RATE OF RAFFINATE TAKEOF AT A SUBSTANTIAL CONSTANT VALUE AND MEANS FOR VARYING THE SOLVENT INPUT RATE IN RESPONSE TO THE RISE AND FALL OF AN INTERFACE BETWEEN SOLVENT AND RAFFINATE PHASES SO AS TO STABILIZE SAID INTERFACE. 